1. Field of the Invention
This invention relates to the provision of air permeable composites for use in the fabrication of filters, and is particularly concerned with the provision of flexible, air permeable fabric formed of a flexible non-woven substrate, organic fibers and solid particles.
This invention provides novel composites, particularly useful in the preparation of fabric filters which are flexible and highly absorbent, and which are advantageous for high throughput and low pressure drop applications; and also provides a method of entrapping small sorptive particles.
2. Description of the Prior Art
Synthetic fibers, both woven and non-woven, are well known and have been used in countless applications for some period of time. Many of these fabrics may be characterized as composites in that they are comprised of two or more distinctively different materials that are bound together in some manner to provide a single material whose properties differ from that of either of its constituent elements. Typical applications for these fabrics or composites include, but are not limited to, the fabrication of protective clothing, filters, screens, protective shields, and numerous decorative items.
Of particular interest in this art is the use of fabrics and/or composites in the fabrication of filters or chemically absorptive cloth-like materials, such as articles of protective clothing for chemical environments.
U.S. Pat. No. 4,127,624 to Keller et al., assigned to the present assignee, discloses production of polymeric fibers and fiber masses from solutions of fiber-forming organic polymers, such as polypropylene, by simultaneously cooling and agitating the polymer solution while subjecting the solution to the application of sonic vibrations, followed by removing the solvent, leaving resultant fiber masses. Fiber bundles produced from masses of this type can be used to form a variety of articles, as for example, to form fabrics.
U.S. Pat. No. 3,971,373 discloses a porous sheet product comprising a web of entangled organic polymeric fibers, such as polypropylene, and an array of solid particles, such as activated carbon, uniformly dispersed and held in the web.
U.S. Pat. No. 4,397,907 to R. W. Rosser and L. B. Keller, assigned to the present assignee, discloses composites fabricated using solid sorptive particles, such as activated charcoal, positioned within a network of organic fibers such as polypropylene fibers. This patent further discloses a woven cloth substrate fiberized with polypropylene and activated charcoal.
However, there exists a requirement for the provision of composite materials, particularly useful as flexible, air permeable filters which permit absorption and entrapment of smaller particles and greater amounts of sorptive particles than current materials, such as those materials taught in the prior art noted above. There is also a need to provide such materials which also provide high flexibility and air permeability, and high sorptive particle, e.g. carbon particle, entrapment levels not available using woven substrate materials, as disclosed in the above-discussed U.S. Pat. No. 4,397,907.
Another area of important utility for composites of this nature is in air filters for filtering out foreign impurities, as for example, for use in various sealed vehicles, e.g. so-called "armored cars." Thus, in these vehicles, a very large filter is employed for drawing air in from the outside. An effective filter of substantially reduced size could be used for this purpose. Also, filters of this general type are needed for use in removing industrial toxins.